From 92009b7f989f83f83159a43574ce5e36b7c4d5a1 Mon Sep 17 00:00:00 2001 From: Felix Fietkau Date: Sat, 7 Apr 2018 10:43:48 +0200 Subject: [PATCH] utils: ensure that byte-order conversion functions evaluate the argument only once Signed-off-by: Felix Fietkau --- utils.h | 40 ++++++++++++++++++++++++---------------- 1 file changed, 24 insertions(+), 16 deletions(-) diff --git a/utils.h b/utils.h index aa480e2..6a53b3f 100644 --- a/utils.h +++ b/utils.h @@ -117,21 +117,29 @@ int clock_gettime(int type, struct timespec *tv); (((uint64_t)(x) & (uint64_t)0x00ff000000000000ULL) >> 40) | \ (((uint64_t)(x) & (uint64_t)0xff00000000000000ULL) >> 56))) +/* + * This returns a constant expression while determining if an argument is + * a constant expression, most importantly without evaluating the argument. + */ +#define __is_constant(x) \ + (sizeof(int) == sizeof(*(1 ? ((void*)((long)(x) * 0l)) : (int*)1))) -static inline uint16_t __u_bswap16(uint16_t val) -{ - return ((val >> 8) & 0xffu) | ((val & 0xffu) << 8); -} +#define __eval_once(func, x) \ + ({ typeof(x) __x = x; func(__x); }) + +#define __eval_safe(func, x) \ + __builtin_choose_expr(__is_constant(x), \ + func(x), __eval_once(func, x)) #if __BYTE_ORDER == __LITTLE_ENDIAN -#define cpu_to_be64(x) __constant_swap64(x) -#define cpu_to_be32(x) __constant_swap32(x) -#define cpu_to_be16(x) __constant_swap16(x) +#define cpu_to_be64(x) __eval_safe(__constant_swap64, x) +#define cpu_to_be32(x) __eval_safe(__constant_swap32, x) +#define cpu_to_be16(x) __eval_safe(__constant_swap16, x) -#define be64_to_cpu(x) __constant_swap64(x) -#define be32_to_cpu(x) __constant_swap32(x) -#define be16_to_cpu(x) __constant_swap16(x) +#define be64_to_cpu(x) __eval_safe(__constant_swap64, x) +#define be32_to_cpu(x) __eval_safe(__constant_swap32, x) +#define be16_to_cpu(x) __eval_safe(__constant_swap16, x) #define cpu_to_le64(x) (x) #define cpu_to_le32(x) (x) @@ -143,13 +151,13 @@ static inline uint16_t __u_bswap16(uint16_t val) #else /* __BYTE_ORDER == __LITTLE_ENDIAN */ -#define cpu_to_le64(x) __constant_swap64(x) -#define cpu_to_le32(x) __constant_swap32(x) -#define cpu_to_le16(x) __constant_swap16(x) +#define cpu_to_le64(x) __eval_safe(__constant_swap64, x) +#define cpu_to_le32(x) __eval_safe(__constant_swap32, x) +#define cpu_to_le16(x) __eval_safe(__constant_swap16, x) -#define le64_to_cpu(x) __constant_swap64(x) -#define le32_to_cpu(x) __constant_swap32(x) -#define le16_to_cpu(x) __constant_swap16(x) +#define le64_to_cpu(x) __eval_safe(__constant_swap64, x) +#define le32_to_cpu(x) __eval_safe(__constant_swap32, x) +#define le16_to_cpu(x) __eval_safe(__constant_swap16, x) #define cpu_to_be64(x) (x) #define cpu_to_be32(x) (x) -- 2.30.2